With the increased demand on high-speed wireless communications, more spectrum resources are required for transmissions. To improve spectrum efficiency, novel transmission schemes, such as interference alignment, have been proposed to allow new links to access channels if an existing link is not interfered. The schemes include using unused spatial dimensions of the existing link. Instead of using spatial dimensions, subspace frequency division multiplexing has also been proposed, such as exploiting extra dimensions of cyclic prefix (CP) of orthogonal frequency-division multiplexing (OFDM) in an existing link. Such scheme uses single-antenna systems. This scheme may have improved performance over the spatial dimension exploiting scheme but performance is limited by the length of CP. To further improve the system performance, there is a need for a scheme that can exploit both spatial dimensions and frequency division, such as for multiple-input and multiple-output (MIMO) and OFDM systems.